The present invention relates to a device for data transmission to a common communications medium comprising a main station and a plurality of subscribers, which is controllable by transmission of data packets from the main station to the subscribers (downlink) and from the subscribers to the main station (uplink). A method, which is based on one such device, has already been proposed in German Patent Application DE 197 26 120.5. There the main station performs coordinating operations for communications medium access by means of protocol-oriented transmission frames, with signaling periods designated therein. In these transmission frames respective signaling data phases are provided for the uplink and downlink as well as the useful signal data phases.
In centrally controlled mobile radio communication systems, such as GSM, a transmission from the central base station to the reachable subscriber terminals is necessary, during which relevant information is transmitted for all mobile subscribers. Furthermore this information includes the capabilities of the base station, the used frequencies, information relating to sleep mode as well as much other information. This type of information is frequently collected in one logical channel. It is designated as broadcast channel BCH in GSM or the ETSI project HIPERLAN or also as downlink signaling.
In one such communication system one or more subscriber terminals exchange data packets with each other or with the main station by means of a common channel.
Possible communications media include a radio channel, a passive optical network with simple optical splitters and a cable distributive network with coaxial cables and/or glass fibers. The principal is illustrated in FIG. 1. A concentrator with several terminals may replace a single terminal unit (private branch exchange a network unit owned by the operating company). In the following the generality of the terminals is stated without limitation. The subscriber or their terminal is designated with 1, the common transmission medium with 2, the main station with 3 and the transmission network with 4.
The following embodiments were developed for use in ATM networks, but can also be used in other networks, such as IP (internet protocol) or ether networks.
In a centrally controlled communication system it is necessary to build a structure into the medium, which permits the terminals to be synchronized to the main station. Furthermore in central control the main station must administer the commonly used medium and assign or refer to the respective terminal. For that purpose medium access protocols (Medium access control, MAC) are suitable. These medium access protocols are described in D. Petras, A. Krxc3xa4mling, xe2x80x9cMAC Protocol with Polling and Fast Collision Resolution for an ATM Air Interfacexe2x80x9d, IEEE ATM Workshop, San Franciso, Calif., August 1996, and in D. Petras, A. Krxc3xa4mling, A. Hettich, xe2x80x9cMAC Protocol for Wireless ATM Contention Free Versus Contention Based Transmission of Reservation Requestsxe2x80x9d, PIMRC ""96, Taipei, Taiwan, October 1996.
It is an object of the present invention to provided an improved more efficient device for data transmission of the above-described kind.
The device with the features of the invention allows an efficient information transmission, especially in the signaling data phase for the downlink (broadcast channel). Data that must be transmitted in each transmission frame, can be separated from data which must be only sporadically or only seldom available by distributing the data into two different types of data fields. For the latter type of data the data field is not assigned certain fixed types of information, but can be used for different information elements from the main station as required. Because of that feature a widely variable data rate is available for various information elements.
In order to identify the type of information elements they are provided with a header for identification purposes. Possible content of the information elements include, e.g., announcements of frequency changes, information regarding terminals in the sleep mode, status information, additions to manufacture-specific information or information regarding the capabilities of the main station.
A flexible adjustment and/or expansion to future requirements is possible by means of the division of the data fields according to the invention. It is also possible to transmit hardly any information in the second data field and e.g. to perform measurements of the radio background during this time.
In contrast to the situation in the prior art, according to the invention space does not need to be provided in each transmission frame for information that is not continuously required. Furthermore in the solutions according to the prior art expandability is only possible by reservation of additional data capacity.